I have two 2nd gen Speed Concepts, both are AXS 12 Speed GXP.
Works perfectly fine!
Be aware - GXP is a dying standard, and the new Sram line will not offer any GXP cranks.
So grab the last Red cranks out there, or you end up buying used.

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I love rim brake bikes!

Thanks for that. How does it work from a cassette selection since I assume the GXP rings are different than the newer ones with Dub. I.e. 35/48 vs 34/50

That’s a bit involved.
Your Shimano stuff will not work anymore if you go Sram 12 speed (road).
You need a new freehub (XDR), new cassette (Sram 12 speed XDR), new chain (Flat Top), and rings.
For triathlon I’d go at least 50/37, if not bigger. Or, ditch the FD and go 1x. Much cleaner and still usable for climbs with the right ring/cassette combo.
I have a 50t on one bike, and a 48t on the other. Both are 1x setups.
On flat courses I run a 10-28 cassette, if there are serious climbs, I swap to a 10-33 and might even take the bike with the 48 ring for that race.

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I love rim brake bikes!

If you go with an Apex 12-speed cassette, you can use your existing 11-sp driver body and you don't need to swap freehubs to XDR. Just throwing that out there.

https://www.sram.com/...models/cs-pg-1130-a1

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the world's still turning? >>>>>>> the world's still turning

So I understood I’d need to go all SRAM if I went this direction, but 2x is my only option. Not going to have the strength to ride a 1x system. So if I went GXP chainrings does that mess up the intent of AXS with the cassette combo expecting smaller rings? Thinking I would face a similar situation to the Shimano crank/cassette gearing issues I have now where I can’t trim it the way it should be.

What am I missing? I only see an 11speed cassette?

you're right - I wasn't reading that properly it is only 11-sp. my bad!

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the world's still turning? >>>>>>> the world's still turning

The GXP crank will accept the exact same direct mount, 8-bolt interface chainring(s) as any current Sram crankset. It’s basically the same crank as the dub version, just with a different spindle setup.

If you go std 2x setup, your options are 46/33, 48/35, 50/37, and 52/39.
You can mount any Red or Force Direct mount, 8-bolt interface chainring!
(1x, 2x, Power Meter, even aftermarket stuff like Stone, or Garbaruk).

The nice thing about the XDR cassettes (available in Rival, Force, and Red) is the size of the smallest cog (10t) which allows for running a smaller chainring in the front without redlining when it comes to your cadence at high speeds.

You should read a bit about AXS, Sram has tons of good info on their site.

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I love rim brake bikes!

I use a SRAM Force 11 crankset with a direct mount 1x chainring. There is a Red version too, but costs a little more.

In terms of cassette, I use a Shimano HG compatible (aka the old style SRAM/Shimano hub) cassette since the SRAM 12 speed uses a new hub style.

My current setup is 1x with an aero Stone 54t up front direct mounted to a SRAM Force11 crankset and running a HG compatible 12-30 on the rear.